Current understanding of CNS regeneration in man, our ability to assess and promote specific regrowth of axons and reestablishment of functional synaptic relations, is limited by a general ignorance of the cellular mechanisms underlying general nerve growth and synaptic selectivity. Using a lower vertebrate model (retinotectal connections of the frog Xenopus), we have developed novel neuroplasticity settings in which retinal axons rewire connections with neurons. The unique accessibility of the system, and the unique opportunity its development holds for systematically breaking down its components, have allowed us to study fiber-cell relationships that drive the rewiring in a controlled causal analysis that combines surgery, electrophysiology, anatomy, embryology, cell biology and biochemistry. We propose to study the roles of fiber-target affinity, fiber-fiber competition, and position effects in the formation, regeneration and translocation of retinotectal synapses by a unique post-synaptic single-cell technique. We propose to further characerize the develomental signals that modify the synaptic specificities which optic fibers differentiate, with the hope of identifying mechanisms capable of modulating synaptic affinities in adult neurons. Finally, we propose further studies on these specificity properties themselves, and their informational, cellular and molecular basis. The proposed studies are based on detailed pilot data already obtained and offer clear pathways into synaptogenic mechanisms.